Clinical lung maturation is frequent in very low birth weight preterm infants and early lung maturation is associated clinically with the chronic chorioamnionitis that seems to cause preterm delivery. Intra-amniotic endotoxin causes chorioamnionitis, lung inflammation and striking lung maturation in fetal sheep. Intra-amniotic IL-1 also causes lung maturation, and both IL-1 and endotoxin induce the lung maturation response by direct contact with the fetal lung and not by inducing a systemic response. Other inflammatory mediators such as TNFalpha and IFNgamma have no effect on the fetal lung. Preliminary data suggest that the fetal airways produce mediators that recruit (IL-8) W that recruit WBC to the fetal lungs and that those cells then amplify the maturation signal, which may be IL-1beta, resulting in increased surfactant and lung structural changes. This proposal explores the pathways leading from the intra-amniotic pro-inflammatory mediator to lung maturation using the fetal sheep model. Experiments will test if IL-1 is the proximal mediator of lung maturation, if IL-8 produced by the airway recruits WBC to the fetal lungs, if those cells are required for lung maturation, and if these pathways are NFKappaB dependent. The innate host response to inflammation is mediated by receptors for pathogen component recognition domains, the Toll-Like Receptors (TLRs). There is no information about TLR function in the fetus. Because chorioamnionitis is caused by different organisms, we will characterize the fetal lung responses to intra-amniotic TLR agonists for TLR2, TLR3, TLR4, TLR5 and TLR9. These data together with identification of the signaling pathways for endotoxin (TLR4)/IL-1 will elucidate the links between antenatal infection and lung maturation. A goal is to identify a mediator with potential for clinical use to induce lung maturation.